The objectives of this proposal are to define the mechanisms by which chronic Helicobacter infection leads to the development of preneoplastic gastric epithelium, using a novel animal model, Helicobacter felis-infected interleukin 10-deficient mice (IL10-/-). Helicobacter pylori infection is the major etiologic agent of peptic ulcer disease, and chronic H. pylori infection can lead to the development of preneoplastic gastric epithelium and gastric cancer. Observations in this application demonstrate that Helicobacter felis infected IL-10 deficient mice develop severe chronic inflammation and preneoplastic gastric epithelium. The overall hypothesis of this application is that absence of IL-10 results in the development of a dysregulated immune/inflammatory response to Helicobacter. The chronic, severe inflammation in H. felis-infected IL10-/- mice leads to dysregulated production of growth mediators which alters the normal growth and differentiation of gastric epithelium resulting in the development of preneoplastic gastric epithelium. The specific aims of the project are: (1) Characterize the immune and inflammatory response to H. felis in wild-type and IL10-/- mice. The composition of the inflammatory infiltrate in H. felis-infected wild-type and IL10-/- mice will be defined using immunohistochemistry and flow cytometry. The role of immune cell types in H. felis infection will be evaluated using mice deficient in B cells (IL10-/-/Bcell-/-), B and T cells (IL10-/-Rag2-/-), and neutrophil-depleted IL10-/- mice. Cytokine mediators in H. felis-infected IL10-/-mice will be assessed via (a) inhibition of cytokines with neutralizing antibodies; (b) inhibition of prostaglandin production using a cyclooxygenase inhibitor; and (c) the role of NO will be assessed through use of IL10-/-NOS-/- mice. (2) Characterize the epithelial phenotype in H. felis infected IL10-/- mice. Northern blot, RNAse protection, and in situ hybridization with lineage specific markers will be used to assess epithelial differentiation in H. felis-infected IL10-/- mice. Proliferation and apoptosis in the development of preneoplastic epithelium will also be assessed. (3) Define the role of candidate growth factors and their receptors in the development of preneoplastic epithelium in H. felis-infected IL10-/- mice. Northern blot analysis, RNAse protection assays, and in situ hybridization techniques will be used to evaluate the level and spatial pattern of growth factor and growth factor receptor expression. Characterization of this model of Helicobacter-induced preneoplasia will enhance our understanding of the mechanism by which chronic H. pylori infection leads to gastric cancer in humans and may lead to new strategies for the prevention of gastric ulcer.